全文获取类型
收费全文 | 1557篇 |
免费 | 67篇 |
国内免费 | 2篇 |
专业分类
化学 | 1011篇 |
晶体学 | 6篇 |
力学 | 19篇 |
数学 | 224篇 |
物理学 | 366篇 |
出版年
2023年 | 12篇 |
2022年 | 17篇 |
2021年 | 46篇 |
2020年 | 40篇 |
2019年 | 43篇 |
2018年 | 29篇 |
2017年 | 29篇 |
2016年 | 77篇 |
2015年 | 50篇 |
2014年 | 62篇 |
2013年 | 66篇 |
2012年 | 126篇 |
2011年 | 145篇 |
2010年 | 109篇 |
2009年 | 65篇 |
2008年 | 102篇 |
2007年 | 136篇 |
2006年 | 80篇 |
2005年 | 68篇 |
2004年 | 55篇 |
2003年 | 37篇 |
2002年 | 30篇 |
2001年 | 10篇 |
2000年 | 6篇 |
1999年 | 9篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 15篇 |
1995年 | 21篇 |
1994年 | 20篇 |
1993年 | 14篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 3篇 |
1989年 | 6篇 |
1987年 | 7篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1982年 | 4篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1975年 | 2篇 |
1969年 | 2篇 |
1968年 | 2篇 |
1905年 | 3篇 |
1904年 | 2篇 |
排序方式: 共有1626条查询结果,搜索用时 15 毫秒
41.
42.
43.
Headphone rendering of nearby virtual sound sources represents to date an open issue in 3-D audio, due to a number of technical challenges and temporal requirements involved in the measurement of individual Head-Related Transfer Functions (HRTFs). In order to tackle this problem, we propose a filter model of near-field effects based on the Distance Variation Function (Kan et al., 2009). Thanks to its simple structure and low order, the model can be applied to any far-field virtual auditory display to yield a realistic and computationally efficient near-field compensation of spectral and binaural effects. The model is subjectively evaluated in two psychophysical experiments where the relative distance of pairs of virtually rendered sound sources is judged. Results show that even though sound intensity overshadows subtler near-field effects when it is available as a cue for distance, the model is capable of offering relative distance information of near lateral virtual sources when intensity cues are removed. Furthermore, performances of the model in relative distance rendering are compared to those of alternative near-field rendering methods available in the literature. 相似文献
44.
Dr. Thies Olaf Petersen Dustin Simone Prof. Dr. Ingo Krossing 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(44):15847-15855
Attempts to prepare previously unknown simple and very Lewis acidic [RZn]+[Al(ORF)4]? salts from ZnR2, AlR3, and HO?RF delivered the ion‐like RZn(Al(ORF)4) (R=Me, Et; RF=C(CF3)3) with a coordinated counterion, but never the ionic compound. Increasing the steric bulk in RZn+ to R=CH2CMe3, CH2SiMe3, or Cp*, thus attempting to induce ionization, failed and led only to reaction mixtures including anion decomposition. However, ionization of the ion‐like EtZn(Al(ORF)4) compound with arenes yielded the [EtZn(arene)2]+[Al(ORF)4]? salts with arene=toluene, mesitylene, or o‐difluorobenzene (o‐DFB)/toluene. In contrast to the ion‐like EtZn(η3‐C6H6)(CHB11Cl11), which co‐crystallizes with one benzene molecule, the less coordinating nature of the [Al(ORF)4]? anion allowed the ionization and preparation of the purely organometallic [EtZn(arene)2]+ cation. These stable materials have further applications as, for example, initiators of isobutene polymerization. DFT calculations to compare the Lewis acidities of the zinc cations to those of a large number of organometallic cations were performed on the basis of fluoride ion affinity. The complexation energetics of EtZn+ with arenes and THF was assessed and related to the experiments. 相似文献
45.
R. R. Silva L. A. Vieira Mendes K. H. Tsui R. A. De Simone Zanon A. L. de Oliveira C. E. Fellows 《Applied physics. B, Lasers and optics》2011,104(3):679-687
Nitrogen laser performance with TE configuration and wedge electrodes is analyzed with background ionization in the laser
discharge channel by α particles at a low exposition rate. With the bias ionization, the laser power presents two peaks as a function of gas pressure,
with one at the normal low pressure, without bias ionization, and the other at high pressure generated by bias ionization.
A simple theoretical model has been developed in a trial to understand this behavior. This model was first tested in later
results for a TE configuration nitrogen laser, with flat electrodes, without and with bias ionization. It has been observed
that due to the competition between electrode shielding by positively charged α particles and bulk ionization by impact, the laser energy is suppressed with pressure below 50 Torr and enhanced above it. 相似文献
46.
Simone Zanotto Francesco Morichetti Andrea Melloni 《Laser \u0026amp; Photonics Reviews》2015,9(6):666-673
Amplitude and phase are the basic properties of all wave phenomena; as far as optical waves are concerned, the ability to act on these variables is at the root of a wealth of switching devices. To quantify the performance of an optical switching device, an essential aspect is to determine the tradeoff between the insertion loss and the amplitude or phase modulation depth. Here it is shown that every optical switching device is subject to such a tradeoff, intrinsically connected to the dielectric response of the materials employed inside the switching element itself. This limit finds its roots in fundamental physics, as it directly derives from Maxwell's equations for linear dielectrics, and is hence applicable to a wide class of optical components. Furthermore, a result is that concepts such as filtering, resonance, and critical coupling could be of advantage in approaching the limit.
47.
Annali di Matematica Pura ed Applicata (1923 -) - Let $$\mathcal X $$ be a flat analytic groupoid $$R_X\stackrel{s}{\underset{t}{\rightrightarrows }}X$$ such that the holomorphic map... 相似文献
48.
49.
We categorify the notion of an infinitesimal braiding in a linear strict symmetric monoidal category, leading to the notion of a (strict) infinitesimal 2-braiding in a linear symmetric strict monoidal 2-category. We describe the associated categorification of the 4-term relations, leading to six categorified relations. We prove that any infinitesimal 2-braiding gives rise to a flat and fake flat 2-connection in the configuration space of n particles in the complex plane, hence to a categorification of the Knizhnik–Zamolodchikov connection. We discuss infinitesimal 2-braidings in a certain monoidal 2-category naturally assigned to every differential crossed module, leading to the notion of a symmetric quasi-invariant tensor in a differential crossed module. Finally, we prove that symmetric quasi-invariant tensors exist in the differential crossed module associated to Wagemann's version of the String Lie-2-algebra. As a corollary, we obtain a more conceptual proof of the flatness of a previously constructed categorified Knizhnik–Zamolodchikov connection with values in the String Lie-2-algebra. 相似文献
50.
We consider extensions of certain states. The states are defined on the systems of sets that are closed under the formation of the symmetric difference (concrete quantum logics). These systems can be viewed as certain set‐representable quantum logics enriched with the symmetric difference. We first show how the compactness argument allows us to extend states on Boolean algebras over such systems of sets. We then observe that the extensions are sometimes possible even for non‐Boolean situations. On the other hand, a difference‐closed system can be constructed such that even two‐valued states do not allow for extensions. Finally, we consider these questions in a σ‐complete setup and find a large class of such systems with rather interesting state properties. 相似文献